Isotropic superconducting state and high critical currents in Fe1+yTe1-xSx single crystals

Abstract

We report single crystal growth and a study of superconducting properties in Fe_{1+y}Te_{1-x}S_{x}. We demonstrate the smallest upper critical field anisotropy, gamma=H_{c2}^{//c}/H_{c2}^{//a}, among all iron based superconductors, the value of gamma reaches 1.05 at T=0.65T_{C} for Fe_{1.09}Te_{0.89}S_{0.11}, while still maintaining large values of upper critical field.